# -*- coding:utf-8 -*-
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# Copyright 2016 The Android Open Source Project
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Signal related functionality."""
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from __future__ import print_function
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import os
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import signal
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import sys
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_path = os.path.realpath(__file__ + '/../..')
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if sys.path[0] != _path:
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sys.path.insert(0, _path)
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del _path
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def relay_signal(handler, signum, frame):
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"""Notify a listener returned from getsignal of receipt of a signal.
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Returns:
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True if it was relayed to the target, False otherwise.
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False in particular occurs if the target isn't relayable.
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"""
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if handler in (None, signal.SIG_IGN):
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return True
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elif handler == signal.SIG_DFL:
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# This scenario is a fairly painful to handle fully, thus we just
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# state we couldn't handle it and leave it to client code.
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return False
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handler(signum, frame)
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return True
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def signal_module_usable(_signal=signal.signal, _SIGUSR1=signal.SIGUSR1):
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"""Verify that the signal module is usable and won't segfault on us.
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See http://bugs.python.org/issue14173. This function detects if the
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signals module is no longer safe to use (which only occurs during
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final stages of the interpreter shutdown) and heads off a segfault
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if signal.* was accessed.
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This shouldn't be used by anything other than functionality that is
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known and unavoidably invoked by finalizer code during python shutdown.
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Finally, the default args here are intentionally binding what we need
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from the signal module to do the necessary test; invoking code shouldn't
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pass any options, nor should any developer ever remove those default
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options.
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Note that this functionality is intended to be removed just as soon
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as all consuming code installs their own SIGTERM handlers.
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"""
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# Track any signals we receive while doing the check.
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received, actual = [], None
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def handler(signum, frame):
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received.append([signum, frame])
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try:
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# Play with sigusr1, since it's not particularly used.
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actual = _signal(_SIGUSR1, handler)
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_signal(_SIGUSR1, actual)
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return True
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except (TypeError, AttributeError, SystemError, ValueError):
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# The first three exceptions can be thrown depending on the state of the
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# signal module internal Handlers array; we catch all, and interpret it
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# as if we were invoked during sys.exit cleanup.
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# The last exception can be thrown if we're trying to be used in a
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# thread which is not the main one. This can come up with standard
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# python modules such as BaseHTTPServer.HTTPServer.
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return False
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finally:
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# And now relay those signals to the original handler. Not all may
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# be delivered- the first may throw an exception for example. Not our
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# problem however.
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for signum, frame in received:
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actual(signum, frame)
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